Add and link article about cross compiling binutils

rust-os/cross-compile-binutils.md

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+---
+layout: page
+title: Cross Compile Binutils
+category: "rust-os"
+---
+The [GNU Binutils] are a collection of various binary tools such as `ld`, `as`, `objdump`, or `readelf`. These tools are platform-specific, so you need to compile them again if your host system and target system are different. In our case, we need `ld` and `objdump` for the x86_64 architecture.
+[GNU Binutils]: https://www.gnu.org/software/binutils/
+
+## Building Setup
+First, you need to download a current binutils version from [here][download] \(the latest one is near the bottom). After extracting, you should have a folder named `binutils-2.X` where `X` is for example `25.1`. Now can create and switch to a new folder for building (recommended):
+[download]: ftp://sourceware.org/pub/binutils/snapshots
+
+```bash
+mkdir build-binutils
+cd build-binutils
+```
+
+## Configuration
+We execute binutils's `configure` and pass a lot of arguments to it (replace the `X` with the version number):
+
+```bash
+../binutils-2.X/configure --target=x86_64-elf --prefix="$HOME/opt/cross" \
+    --disable-nls --disable-werror \
+    --disable-gdb --disable-libdecnumber --disable-readline --disable-sim
+```
+- The `target` argument specifies the the x86_64 target architecture.
+- The `prefix` argument selects the installation directory, you can change it if you like. But be careful that you do not overwrite your system's binutils.
+- The `disable-nls` flag disables native language support (so you'll get the same english error messages). It also reduces build dependencies.
+- The `disable-werror` turns all warnings into errors.
+- The last line disables features we don't need to reduce compile time.
+
+## Building it
+Now we can build and install it to the location supplied as `prefix` (it will take a while):
+
+```bash
+make
+make install
+```
+Now you should have multiple `x86_64-elf-XXX` files in `$HOME/opt/cross/bin`.
+
+## Adding it to the PATH
+To use the tools from the command line easily, you should add the `bin` folder to your PATH:
+
+```bash
+export PATH="$HOME/opt/cross/bin:$PATH"
+```
+If you add this line to your e.g. `.bashrc`, the `x86_64-elf-XXX` commands are always available.